Heretofore, it has been well known to form orthodontic appliances of elastomeric material and to mold orthodontic ligatures of elastic urethane, such as shown in U.S. Pat. No. 3,530,583. Similarly, U.S. Pat. Nos. 3,758,947 and 4,900,250 also disclose the molding of orthodontic elastomeric appliances.
It has also been known to coat elastomeric medical devices with a hydrophillic film as shown in U.S. Pat. Nos. 4,100,309 and 4,642,267 so that the medical appliances when wet have a low coefficient of friction and are hydrophillic.
Orthodontic treatment of patients nearly always involves the use of metal, ceramic or plastic brackets in combination with metal archwires. The brackets are provided with archwire slots and tie wings for receiving ligatures to retain the archwires on the brackets. Generally, these ligatures are made of elastomeric material, including polyurethane, as above mentioned. Polyurethane ligatures exhibit a high contact adhesiveness to metal archwires. This contact adhesiveness creates an opposing force and inhibits the movement of brackets along an archwire, thereby increasing treatment time. This problem created by the ligatures has been addressed in the design of self-ligating brackets and other specialty brackets. However, such specialty brackets produce other problems such as loss of rotational control and the inability to use ligatures for cosmetic purposes.